From 62063121620771b4c9cc3e66d883050e4f82378b Mon Sep 17 00:00:00 2001
From: Aaron Robinson <arobins@microsoft.com>
Date: Wed, 11 May 2022 15:39:54 -0700
Subject: [PATCH 01/11] Add BStrStringMarshaller to source generator

---
 .../System.Private.CoreLib.Shared.projitems   |   1 +
 .../Marshalling/BStrStringMarshaller.cs       | 120 ++++++++++++++++++
 .../MarshallingAttributeInfo.cs               |  39 +++---
 .../TypeNames.cs                              |   1 +
 .../ref/System.Runtime.InteropServices.cs     |  14 ++
 .../StringTests.cs                            |  77 +++++++++++
 .../Compiles.cs                               |   2 +
 .../tests/TestAssets/NativeExports/Strings.cs |  62 +++++++++
 8 files changed, 296 insertions(+), 20 deletions(-)
 create mode 100644 src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs

diff --git a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
index 48c1fbecb3fb4f..3d9b0374b78418 100644
--- a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
+++ b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
@@ -867,6 +867,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\InteropServices\MarshalDirectiveException.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\InteropServices\Marshalling\AnsiStringMarshaller.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\InteropServices\Marshalling\ArrayMarshaller.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\InteropServices\Marshalling\BStrStringMarshaller.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\InteropServices\Marshalling\CustomTypeMarshallerAttribute.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\InteropServices\Marshalling\CustomTypeMarshallerDirection.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\InteropServices\Marshalling\CustomTypeMarshallerFeatures.cs" />
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs
new file mode 100644
index 00000000000000..93577e321b7ab2
--- /dev/null
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs
@@ -0,0 +1,120 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Diagnostics;
+using System.Runtime.CompilerServices;
+using System.Text;
+
+namespace System.Runtime.InteropServices.Marshalling
+{
+    /// <summary>
+    /// Marshaller for BSTR strings
+    /// </summary>
+    [CLSCompliant(false)]
+    [CustomTypeMarshaller(typeof(string), BufferSize = 0x200,
+        Features = CustomTypeMarshallerFeatures.UnmanagedResources | CustomTypeMarshallerFeatures.TwoStageMarshalling | CustomTypeMarshallerFeatures.CallerAllocatedBuffer)]
+    public unsafe ref struct BStrStringMarshaller
+    {
+        private byte* _ptrToFirstChar;
+        private bool _allocated;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="BStrStringMarshaller"/>.
+        /// </summary>
+        /// <param name="str">The string to marshal.</param>
+        public BStrStringMarshaller(string? str)
+            : this(str, default)
+        { }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="BStrStringMarshaller"/>.
+        /// </summary>
+        /// <param name="str">The string to marshal.</param>
+        /// <param name="buffer">Buffer that may be used for marshalling.</param>
+        /// <remarks>
+        /// The <paramref name="buffer"/> must not be movable - that is, it should not be
+        /// on the managed heap or it should be pinned.
+        /// <seealso cref="CustomTypeMarshallerFeatures.CallerAllocatedBuffer"/>
+        /// </remarks>
+        public BStrStringMarshaller(string? str, Span<byte> buffer)
+        {
+            _allocated = false;
+
+            if (str is null)
+            {
+                _ptrToFirstChar = null;
+                return;
+            }
+
+            int lengthInBytes = checked(sizeof(char) * str.Length);
+
+            // A caller provided buffer must be at least (lengthInBytes + 6) bytes
+            // in order to be constructed manually. The 6 extra bytes are 4 for byte length and 2 for wide null.
+            if ((lengthInBytes + 6) > buffer.Length)
+            {
+                // Use precise byte count when the provided stack-allocated buffer is not sufficient
+                _ptrToFirstChar = (byte*)Marshal.AllocBSTRByteLen((uint)lengthInBytes);
+                _allocated = true;
+            }
+            else
+            {
+                // set length and update buffer target
+                byte* pBuffer = (byte*)Unsafe.AsPointer(ref MemoryMarshal.GetReference(buffer));
+                *((uint*)pBuffer) = (uint)lengthInBytes;
+                _ptrToFirstChar = pBuffer + sizeof(uint);
+            }
+
+            // Confirm the size is properly set for the allocated BSTR.
+            Debug.Assert(lengthInBytes == Marshal.SysStringByteLen((IntPtr)_ptrToFirstChar));
+
+            // Copy characters from the managed string
+            Buffer.Memmove(ref *(char*)_ptrToFirstChar, ref str.GetRawStringData(), (nuint)str.Length + 1);
+        }
+
+        /// <summary>
+        /// Returns the native value representing the string.
+        /// </summary>
+        /// <remarks>
+        /// <seealso cref="CustomTypeMarshallerFeatures.TwoStageMarshalling"/>
+        /// </remarks>
+        public byte* ToNativeValue() => _ptrToFirstChar;
+
+        /// <summary>
+        /// Sets the native value representing the string.
+        /// </summary>
+        /// <param name="value">The native value.</param>
+        /// <remarks>
+        /// <seealso cref="CustomTypeMarshallerFeatures.TwoStageMarshalling"/>
+        /// </remarks>
+        public void FromNativeValue(byte* value)
+        {
+            _ptrToFirstChar = value;
+            _allocated = true;
+        }
+
+        /// <summary>
+        /// Returns the managed string.
+        /// </summary>
+        /// <remarks>
+        /// <seealso cref="CustomTypeMarshallerDirection.Out"/>
+        /// </remarks>
+        public string? ToManaged()
+        {
+            if (_ptrToFirstChar is null)
+                return null;
+            return Marshal.PtrToStringBSTR((IntPtr)_ptrToFirstChar);
+        }
+
+        /// <summary>
+        /// Frees native resources.
+        /// </summary>
+        /// <remarks>
+        /// <seealso cref="CustomTypeMarshallerFeatures.UnmanagedResources"/>
+        /// </remarks>
+        public void FreeNative()
+        {
+            if (_allocated)
+                Marshal.FreeBSTR((IntPtr)_ptrToFirstChar);
+        }
+    }
+}
diff --git a/src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/MarshallingAttributeInfo.cs b/src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/MarshallingAttributeInfo.cs
index 795a49642c0797..c888ca035a9420 100644
--- a/src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/MarshallingAttributeInfo.cs
+++ b/src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/MarshallingAttributeInfo.cs
@@ -12,7 +12,6 @@
 
 namespace Microsoft.Interop
 {
-
     /// <summary>
     /// Type used to pass on default marshalling details.
     /// </summary>
@@ -73,7 +72,6 @@ public enum CharEncoding
         Undefined,
         Utf8,
         Utf16,
-        Ansi,
         Custom
     }
 
@@ -762,7 +760,13 @@ private bool TryCreateTypeBasedMarshallingInfo(
                 }
                 else
                 {
-                    marshallingInfo = CreateStringMarshallingInfo(type, _defaultInfo.CharEncoding);
+                    marshallingInfo = _defaultInfo.CharEncoding switch
+                    {
+                        CharEncoding.Utf16 => CreateStringMarshallingInfo(type, TypeNames.Utf16StringMarshaller),
+                        CharEncoding.Utf8 => CreateStringMarshallingInfo(type, TypeNames.Utf8StringMarshaller),
+                        _ => throw new InvalidOperationException()
+                    };
+
                     return true;
                 }
 
@@ -843,30 +847,25 @@ private MarshallingInfo CreateStringMarshallingInfo(
             ITypeSymbol type,
             UnmanagedType unmanagedType)
         {
-            CharEncoding charEncoding = unmanagedType switch
+            string? marshallerName = unmanagedType switch
             {
-                UnmanagedType.LPStr => CharEncoding.Ansi,
-                UnmanagedType.LPTStr or UnmanagedType.LPWStr => CharEncoding.Utf16,
-                MarshalAsInfo.UnmanagedType_LPUTF8Str => CharEncoding.Utf8,
-                _ => CharEncoding.Undefined
+                UnmanagedType.BStr => TypeNames.BStrStringMarshaller,
+                UnmanagedType.LPStr => TypeNames.AnsiStringMarshaller,
+                UnmanagedType.LPTStr or UnmanagedType.LPWStr => TypeNames.Utf16StringMarshaller,
+                MarshalAsInfo.UnmanagedType_LPUTF8Str => TypeNames.Utf8StringMarshaller,
+                _ => null
             };
-            if (charEncoding == CharEncoding.Undefined)
+
+            if (marshallerName is null)
                 return new MarshalAsInfo(unmanagedType, _defaultInfo.CharEncoding);
 
-            return CreateStringMarshallingInfo(type, charEncoding);
+            return CreateStringMarshallingInfo(type, marshallerName);
         }
 
         private MarshallingInfo CreateStringMarshallingInfo(
             ITypeSymbol type,
-            CharEncoding charEncoding)
+            string marshallerName)
         {
-            string? marshallerName = charEncoding switch
-            {
-                CharEncoding.Ansi => TypeNames.AnsiStringMarshaller,
-                CharEncoding.Utf16 => TypeNames.Utf16StringMarshaller,
-                CharEncoding.Utf8 => TypeNames.Utf8StringMarshaller,
-                _ => throw new InvalidOperationException()
-            };
             INamedTypeSymbol? stringMarshaller = _compilation.GetTypeByMetadataName(marshallerName);
             if (stringMarshaller is null)
                 return new MissingSupportMarshallingInfo();
@@ -877,9 +876,9 @@ private MarshallingInfo CreateStringMarshallingInfo(
             return CreateNativeMarshallingInfoForValue(
                 type,
                 stringMarshaller,
-                default,
+                null,
                 customTypeMarshallerData.Value,
-                allowPinningManagedType: charEncoding == CharEncoding.Utf16,
+                allowPinningManagedType: marshallerName is TypeNames.Utf16StringMarshaller,
                 useDefaultMarshalling: false);
         }
 
diff --git a/src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/TypeNames.cs b/src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/TypeNames.cs
index 876dc649001f97..778c1cd2beb39a 100644
--- a/src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/TypeNames.cs
+++ b/src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/TypeNames.cs
@@ -18,6 +18,7 @@ public static class TypeNames
         public const string CustomTypeMarshallerAttributeGenericPlaceholder = "System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerAttribute.GenericPlaceholder";
 
         public const string AnsiStringMarshaller = "System.Runtime.InteropServices.Marshalling.AnsiStringMarshaller";
+        public const string BStrStringMarshaller = "System.Runtime.InteropServices.Marshalling.BStrStringMarshaller";
         public const string Utf16StringMarshaller = "System.Runtime.InteropServices.Marshalling.Utf16StringMarshaller";
         public const string Utf8StringMarshaller = "System.Runtime.InteropServices.Marshalling.Utf8StringMarshaller";
 
diff --git a/src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs b/src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs
index 6c196e7f100621..9b8cf7383c5f34 100644
--- a/src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs
+++ b/src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs
@@ -2078,6 +2078,20 @@ public void FromNativeValue(byte* value) { }
         public string? ToManaged() { throw null; }
         public void FreeNative() { }
     }
+    [System.CLSCompliant(false)]
+    [System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerAttribute(typeof(string), BufferSize = 0x200,
+        Features = System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerFeatures.UnmanagedResources
+            | System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerFeatures.CallerAllocatedBuffer
+            | System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerFeatures.TwoStageMarshalling )]
+    public unsafe ref struct BStrStringMarshaller
+    {
+        public BStrStringMarshaller(string? str) { }
+        public BStrStringMarshaller(string? str, System.Span<byte> buffer) { }
+        public byte* ToNativeValue() { throw null; }
+        public void FromNativeValue(byte* value) { }
+        public string? ToManaged() { throw null; }
+        public void FreeNative() { }
+    }
     [System.CLSCompliantAttribute(false)]
     [System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerAttribute(typeof(System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerAttribute.GenericPlaceholder[]),
         System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerKind.LinearCollection, BufferSize = 0x200,
diff --git a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/StringTests.cs b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/StringTests.cs
index d9c1f82c8e8d86..00757b1449a5a9 100644
--- a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/StringTests.cs
+++ b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/StringTests.cs
@@ -23,6 +23,7 @@ private class EntryPoints
 
             private const string UShortSuffix = "_ushort";
             private const string ByteSuffix = "_byte";
+            private const string BStrSuffix = "_bstr";
 
             public class Byte
             {
@@ -41,6 +42,15 @@ public class UShort
                 public const string ReverseInplace = EntryPoints.ReverseInplace + UShortSuffix;
                 public const string ReverseReplace = EntryPoints.ReverseReplace + UShortSuffix;
             }
+
+            public class BStr
+            {
+                public const string ReturnLength = EntryPoints.ReturnLength + BStrSuffix;
+                public const string ReverseReturn = EntryPoints.ReverseReturn + BStrSuffix;
+                public const string ReverseOut = EntryPoints.ReverseOut + BStrSuffix;
+                public const string ReverseInplace = EntryPoints.ReverseInplace + BStrSuffix;
+                public const string ReverseReplace = EntryPoints.ReverseReplace + BStrSuffix;
+            }
         }
 
         public partial class Utf16
@@ -185,6 +195,31 @@ public partial class LPStr
             public static partial void Reverse_Replace_Ref([MarshalAs(UnmanagedType.LPStr)] ref string s);
         }
 
+        public partial class BStr
+        {
+            [LibraryImport(NativeExportsNE_Binary, EntryPoint = EntryPoints.BStr.ReturnLength)]
+            public static partial int ReturnLength([MarshalAs(UnmanagedType.BStr)] string s);
+
+            [LibraryImport(NativeExportsNE_Binary, EntryPoint = EntryPoints.BStr.ReturnLength, StringMarshalling = StringMarshalling.Utf16)]
+            public static partial int ReturnLength_IgnoreStringMarshalling([MarshalAs(UnmanagedType.BStr)] string s);
+
+            [LibraryImport(NativeExportsNE_Binary, EntryPoint = EntryPoints.BStr.ReverseReturn)]
+            [return: MarshalAs(UnmanagedType.LPStr)]
+            public static partial string Reverse_Return([MarshalAs(UnmanagedType.BStr)] string s);
+
+            [LibraryImport(NativeExportsNE_Binary, EntryPoint = EntryPoints.BStr.ReverseOut)]
+            public static partial void Reverse_Out([MarshalAs(UnmanagedType.BStr)] string s, [MarshalAs(UnmanagedType.BStr)] out string ret);
+
+            [LibraryImport(NativeExportsNE_Binary, EntryPoint = EntryPoints.BStr.ReverseInplace)]
+            public static partial void Reverse_Ref([MarshalAs(UnmanagedType.BStr)] ref string s);
+
+            [LibraryImport(NativeExportsNE_Binary, EntryPoint = EntryPoints.BStr.ReverseInplace)]
+            public static partial void Reverse_In([MarshalAs(UnmanagedType.BStr)] in string s);
+
+            [LibraryImport(NativeExportsNE_Binary, EntryPoint = EntryPoints.BStr.ReverseInplace)]
+            public static partial void Reverse_Replace_Ref([MarshalAs(UnmanagedType.BStr)] ref string s);
+        }
+
         public partial class StringMarshallingCustomType
         {
             public partial class Utf16
@@ -418,6 +453,48 @@ public void AnsiStringByRef(string value)
             Assert.Equal(expected, refValue);
         }
 
+        [Theory]
+        [MemberData(nameof(UnicodeStrings))]
+        public void BStrStringMarshalledAsExpected(string value)
+        {
+            int expectedLen = value != null ? value.Length : -1;
+
+            Assert.Equal(expectedLen, NativeExportsNE.BStr.ReturnLength(value));
+            Assert.Equal(expectedLen, NativeExportsNE.BStr.ReturnLength_IgnoreStringMarshalling(value));
+        }
+
+        [Theory]
+        [MemberData(nameof(UnicodeStrings))]
+        public void BStrStringReturn(string value)
+        {
+            string expected = ReverseChars(value);
+
+            Assert.Equal(expected, NativeExportsNE.BStr.Reverse_Return(value));
+
+            string ret;
+            NativeExportsNE.BStr.Reverse_Out(value, out ret);
+            Assert.Equal(expected, ret);
+        }
+
+        [Theory]
+        [MemberData(nameof(UnicodeStrings))]
+        public void BStrStringByRef(string value)
+        {
+            string refValue = value;
+            string expected = ReverseChars(value);
+
+            NativeExportsNE.BStr.Reverse_In(in refValue);
+            Assert.Equal(value, refValue); // Should not be updated when using 'in'
+
+            refValue = value;
+            NativeExportsNE.BStr.Reverse_Ref(ref refValue);
+            Assert.Equal(expected, refValue);
+
+            refValue = value;
+            NativeExportsNE.BStr.Reverse_Replace_Ref(ref refValue);
+            Assert.Equal(expected, refValue);
+        }
+
         [Theory]
         [MemberData(nameof(UnicodeStrings))]
         public void StringMarshallingCustomType_MarshalledAsExpected(string value)
diff --git a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/Compiles.cs b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/Compiles.cs
index e62247a20e1b9c..a9da6093b1e7ef 100644
--- a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/Compiles.cs
+++ b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/Compiles.cs
@@ -108,9 +108,11 @@ public static IEnumerable<object[]> CodeSnippetsToCompile()
             yield return new[] { CodeSnippets.MarshalAsParametersAndModifiers<string>(UnmanagedType.LPTStr) };
             yield return new[] { CodeSnippets.MarshalAsParametersAndModifiers<string>(UnmanagedType.LPUTF8Str) };
             yield return new[] { CodeSnippets.MarshalAsParametersAndModifiers<string>(UnmanagedType.LPStr) };
+            yield return new[] { CodeSnippets.MarshalAsParametersAndModifiers<string>(UnmanagedType.BStr) };
             yield return new[] { CodeSnippets.MarshalAsArrayParameterWithNestedMarshalInfo<string>(UnmanagedType.LPWStr) };
             yield return new[] { CodeSnippets.MarshalAsArrayParameterWithNestedMarshalInfo<string>(UnmanagedType.LPUTF8Str) };
             yield return new[] { CodeSnippets.MarshalAsArrayParameterWithNestedMarshalInfo<string>(UnmanagedType.LPStr) };
+            yield return new[] { CodeSnippets.MarshalAsArrayParameterWithNestedMarshalInfo<string>(UnmanagedType.BStr) };
 
             // [In, Out] attributes
             // By value non-blittable array
diff --git a/src/libraries/System.Runtime.InteropServices/tests/TestAssets/NativeExports/Strings.cs b/src/libraries/System.Runtime.InteropServices/tests/TestAssets/NativeExports/Strings.cs
index acb72da759ce53..1610a49069eede 100644
--- a/src/libraries/System.Runtime.InteropServices/tests/TestAssets/NativeExports/Strings.cs
+++ b/src/libraries/System.Runtime.InteropServices/tests/TestAssets/NativeExports/Strings.cs
@@ -26,6 +26,15 @@ public static int ReturnLengthByte(byte* input)
             return GetLength(input);
         }
 
+        [UnmanagedCallersOnly(EntryPoint = "return_length_bstr")]
+        public static int ReturnLengthBStr(byte* input)
+        {
+            if (input == null)
+                return -1;
+
+            return GetLengthBStr(input);
+        }
+
         [UnmanagedCallersOnly(EntryPoint = "reverse_return_ushort")]
         public static ushort* ReverseReturnUShort(ushort* input)
         {
@@ -38,6 +47,12 @@ public static int ReturnLengthByte(byte* input)
             return Reverse(input);
         }
 
+        [UnmanagedCallersOnly(EntryPoint = "reverse_return_bstr")]
+        public static byte* ReverseReturnBStr(byte* input)
+        {
+            return ReverseBStr(input);
+        }
+
         [UnmanagedCallersOnly(EntryPoint = "reverse_out_ushort")]
         public static void ReverseReturnAsOutUShort(ushort* input, ushort** ret)
         {
@@ -50,6 +65,12 @@ public static void ReverseReturnAsOutByte(byte* input, byte** ret)
             *ret = Reverse(input);
         }
 
+        [UnmanagedCallersOnly(EntryPoint = "reverse_out_bstr")]
+        public static void ReverseReturnAsOutBStr(byte* input, byte** ret)
+        {
+            *ret = ReverseBStr(input);
+        }
+
         [UnmanagedCallersOnly(EntryPoint = "reverse_inplace_ref_ushort")]
         public static void ReverseInPlaceUShort(ushort** refInput)
         {
@@ -69,6 +90,17 @@ public static void ReverseInPlaceByte(byte** refInput)
             span.Reverse();
         }
 
+        [UnmanagedCallersOnly(EntryPoint = "reverse_inplace_ref_bstr")]
+        public static void ReverseInPlaceBStr(byte** refInput)
+        {
+            int len = GetLengthBStr(*refInput);
+
+            // Testing of BSTRs is done under the assumption the
+            // test character input size is 16 bit.
+            var span = new Span<ushort>(*refInput, len);
+            span.Reverse();
+        }
+
         [UnmanagedCallersOnly(EntryPoint = "reverse_replace_ref_ushort")]
         public static void ReverseReplaceRefUShort(ushort** s)
         {
@@ -91,6 +123,17 @@ public static void ReverseReplaceRefByte(byte** s)
             *s = ret;
         }
 
+        [UnmanagedCallersOnly(EntryPoint = "reverse_replace_ref_bstr")]
+        public static void ReverseReplaceRefBStr(byte** s)
+        {
+            if (*s == null)
+                return;
+
+            byte* ret = ReverseBStr(*s);
+            Marshal.FreeBSTR((IntPtr)(*s));
+            *s = ret;
+        }
+
         internal static ushort* Reverse(ushort *s)
         {
             if (s == null)
@@ -121,6 +164,17 @@ public static void ReverseReplaceRefByte(byte** s)
             return ret;
         }
 
+        internal static byte* ReverseBStr(byte* s)
+        {
+            if (s == null)
+                return null;
+
+            var arr = Marshal.PtrToStringBSTR((IntPtr)s).ToCharArray();
+            Array.Reverse(arr);
+            var revStr = new string(arr);
+            return (byte*)Marshal.StringToBSTR(revStr);
+        }
+
         private static int GetLength(ushort* input)
         {
             if (input == null)
@@ -150,5 +204,13 @@ private static int GetLength(byte* input)
 
             return len;
         }
+
+        private static int GetLengthBStr(byte* input)
+        {
+            if (input == null)
+                return 0;
+
+            return Marshal.PtrToStringBSTR((IntPtr)input).Length;
+        }
     }
 }

From f4cad5ccb60d98f9a80a0f12c74b5442a760f19e Mon Sep 17 00:00:00 2001
From: Aaron Robinson <arobins@microsoft.com>
Date: Wed, 11 May 2022 17:07:48 -0700
Subject: [PATCH 02/11] Update
 src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/StringTests.cs

Wrong marshalling type.
---
 .../tests/LibraryImportGenerator.Tests/StringTests.cs           | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/StringTests.cs b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/StringTests.cs
index 00757b1449a5a9..c164521b080827 100644
--- a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/StringTests.cs
+++ b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/StringTests.cs
@@ -204,7 +204,7 @@ public partial class BStr
             public static partial int ReturnLength_IgnoreStringMarshalling([MarshalAs(UnmanagedType.BStr)] string s);
 
             [LibraryImport(NativeExportsNE_Binary, EntryPoint = EntryPoints.BStr.ReverseReturn)]
-            [return: MarshalAs(UnmanagedType.LPStr)]
+            [return: MarshalAs(UnmanagedType.BStr)]
             public static partial string Reverse_Return([MarshalAs(UnmanagedType.BStr)] string s);
 
             [LibraryImport(NativeExportsNE_Binary, EntryPoint = EntryPoints.BStr.ReverseOut)]

From 5c6e9554059eb1a4cfc6a3a8b5df1b7e36bee32c Mon Sep 17 00:00:00 2001
From: Aaron Robinson <arobins@microsoft.com>
Date: Wed, 11 May 2022 21:27:44 -0700
Subject: [PATCH 03/11] Change to checked addition

---
 .../InteropServices/Marshalling/BStrStringMarshaller.cs      | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs
index 93577e321b7ab2..c86a6669ba3a23 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs
@@ -50,7 +50,8 @@ public BStrStringMarshaller(string? str, Span<byte> buffer)
 
             // A caller provided buffer must be at least (lengthInBytes + 6) bytes
             // in order to be constructed manually. The 6 extra bytes are 4 for byte length and 2 for wide null.
-            if ((lengthInBytes + 6) > buffer.Length)
+            int manualBstrNeeds = checked(lengthInBytes + 6);
+            if (manualBstrNeeds > buffer.Length)
             {
                 // Use precise byte count when the provided stack-allocated buffer is not sufficient
                 _ptrToFirstChar = (byte*)Marshal.AllocBSTRByteLen((uint)lengthInBytes);
@@ -58,7 +59,7 @@ public BStrStringMarshaller(string? str, Span<byte> buffer)
             }
             else
             {
-                // set length and update buffer target
+                // Set length and update buffer target
                 byte* pBuffer = (byte*)Unsafe.AsPointer(ref MemoryMarshal.GetReference(buffer));
                 *((uint*)pBuffer) = (uint)lengthInBytes;
                 _ptrToFirstChar = pBuffer + sizeof(uint);

From be406c81fd44982cbab7fb78de70d60137f2323c Mon Sep 17 00:00:00 2001
From: Aaron Robinson <arobins@microsoft.com>
Date: Wed, 11 May 2022 21:29:04 -0700
Subject: [PATCH 04/11] Apply suggestions from code review

Co-authored-by: Jan Kotas <jkotas@microsoft.com>
---
 .../InteropServices/Marshalling/BStrStringMarshaller.cs        | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs
index c86a6669ba3a23..8bc078cbe765bc 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs
@@ -69,7 +69,8 @@ public BStrStringMarshaller(string? str, Span<byte> buffer)
             Debug.Assert(lengthInBytes == Marshal.SysStringByteLen((IntPtr)_ptrToFirstChar));
 
             // Copy characters from the managed string
-            Buffer.Memmove(ref *(char*)_ptrToFirstChar, ref str.GetRawStringData(), (nuint)str.Length + 1);
+            str.CopyTo(new Span<char>(_ptrToFirstChar, str.Length));
+            _ptrToFirstChar[str.Length] = '\0'; // null-terminate
         }
 
         /// <summary>

From d52db688143b0533e3eaa046ac25b6f07f4f104d Mon Sep 17 00:00:00 2001
From: Aaron Robinson <arobins@microsoft.com>
Date: Wed, 11 May 2022 21:29:30 -0700
Subject: [PATCH 05/11] Update
 src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/StringTests.cs

---
 .../tests/LibraryImportGenerator.Tests/StringTests.cs           | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/StringTests.cs b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/StringTests.cs
index c164521b080827..e23fe087784ddf 100644
--- a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/StringTests.cs
+++ b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.Tests/StringTests.cs
@@ -216,7 +216,7 @@ public partial class BStr
             [LibraryImport(NativeExportsNE_Binary, EntryPoint = EntryPoints.BStr.ReverseInplace)]
             public static partial void Reverse_In([MarshalAs(UnmanagedType.BStr)] in string s);
 
-            [LibraryImport(NativeExportsNE_Binary, EntryPoint = EntryPoints.BStr.ReverseInplace)]
+            [LibraryImport(NativeExportsNE_Binary, EntryPoint = EntryPoints.BStr.ReverseReplace)]
             public static partial void Reverse_Replace_Ref([MarshalAs(UnmanagedType.BStr)] ref string s);
         }
 

From 74a27447332f85639d5ac80433d1759d25817cac Mon Sep 17 00:00:00 2001
From: Aaron Robinson <arobins@microsoft.com>
Date: Wed, 11 May 2022 21:55:22 -0700
Subject: [PATCH 06/11] Update
 src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs

---
 .../Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs
index 8bc078cbe765bc..f9b61a4b4cb323 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs
@@ -70,7 +70,7 @@ public BStrStringMarshaller(string? str, Span<byte> buffer)
 
             // Copy characters from the managed string
             str.CopyTo(new Span<char>(_ptrToFirstChar, str.Length));
-            _ptrToFirstChar[str.Length] = '\0'; // null-terminate
+            ((char*)_ptrToFirstChar)[str.Length] = '\0'; // null-terminate
         }
 
         /// <summary>

From 7044848fdfa8ce6622d5db9adf5282891a65d393 Mon Sep 17 00:00:00 2001
From: Aaron Robinson <arobins@microsoft.com>
Date: Thu, 12 May 2022 08:33:39 -0700
Subject: [PATCH 07/11] Change native type to ushort.

---
 .../Marshalling/BStrStringMarshaller.cs            | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs
index f9b61a4b4cb323..a62f7528473c15 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs
@@ -15,7 +15,7 @@ namespace System.Runtime.InteropServices.Marshalling
         Features = CustomTypeMarshallerFeatures.UnmanagedResources | CustomTypeMarshallerFeatures.TwoStageMarshalling | CustomTypeMarshallerFeatures.CallerAllocatedBuffer)]
     public unsafe ref struct BStrStringMarshaller
     {
-        private byte* _ptrToFirstChar;
+        private ushort* _ptrToFirstChar;
         private bool _allocated;
 
         /// <summary>
@@ -36,7 +36,7 @@ public BStrStringMarshaller(string? str)
         /// on the managed heap or it should be pinned.
         /// <seealso cref="CustomTypeMarshallerFeatures.CallerAllocatedBuffer"/>
         /// </remarks>
-        public BStrStringMarshaller(string? str, Span<byte> buffer)
+        public BStrStringMarshaller(string? str, Span<ushort> buffer)
         {
             _allocated = false;
 
@@ -54,7 +54,7 @@ public BStrStringMarshaller(string? str, Span<byte> buffer)
             if (manualBstrNeeds > buffer.Length)
             {
                 // Use precise byte count when the provided stack-allocated buffer is not sufficient
-                _ptrToFirstChar = (byte*)Marshal.AllocBSTRByteLen((uint)lengthInBytes);
+                _ptrToFirstChar = (ushort*)Marshal.AllocBSTRByteLen((uint)lengthInBytes);
                 _allocated = true;
             }
             else
@@ -62,7 +62,7 @@ public BStrStringMarshaller(string? str, Span<byte> buffer)
                 // Set length and update buffer target
                 byte* pBuffer = (byte*)Unsafe.AsPointer(ref MemoryMarshal.GetReference(buffer));
                 *((uint*)pBuffer) = (uint)lengthInBytes;
-                _ptrToFirstChar = pBuffer + sizeof(uint);
+                _ptrToFirstChar = (ushort*)(pBuffer + sizeof(uint));
             }
 
             // Confirm the size is properly set for the allocated BSTR.
@@ -70,7 +70,7 @@ public BStrStringMarshaller(string? str, Span<byte> buffer)
 
             // Copy characters from the managed string
             str.CopyTo(new Span<char>(_ptrToFirstChar, str.Length));
-            ((char*)_ptrToFirstChar)[str.Length] = '\0'; // null-terminate
+            _ptrToFirstChar[str.Length] = '\0'; // null-terminate
         }
 
         /// <summary>
@@ -79,7 +79,7 @@ public BStrStringMarshaller(string? str, Span<byte> buffer)
         /// <remarks>
         /// <seealso cref="CustomTypeMarshallerFeatures.TwoStageMarshalling"/>
         /// </remarks>
-        public byte* ToNativeValue() => _ptrToFirstChar;
+        public ushort* ToNativeValue() => _ptrToFirstChar;
 
         /// <summary>
         /// Sets the native value representing the string.
@@ -88,7 +88,7 @@ public BStrStringMarshaller(string? str, Span<byte> buffer)
         /// <remarks>
         /// <seealso cref="CustomTypeMarshallerFeatures.TwoStageMarshalling"/>
         /// </remarks>
-        public void FromNativeValue(byte* value)
+        public void FromNativeValue(ushort* value)
         {
             _ptrToFirstChar = value;
             _allocated = true;

From 4c22b5266ff18e1f40b248c072e88a8385e76022 Mon Sep 17 00:00:00 2001
From: Aaron Robinson <arobins@microsoft.com>
Date: Thu, 12 May 2022 09:00:09 -0700
Subject: [PATCH 08/11] Update System.Runtime.InteropServices.cs

Update ref assembly.
---
 .../ref/System.Runtime.InteropServices.cs                   | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs b/src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs
index 9b8cf7383c5f34..8681fb03854048 100644
--- a/src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs
+++ b/src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs
@@ -2086,9 +2086,9 @@ public void FreeNative() { }
     public unsafe ref struct BStrStringMarshaller
     {
         public BStrStringMarshaller(string? str) { }
-        public BStrStringMarshaller(string? str, System.Span<byte> buffer) { }
-        public byte* ToNativeValue() { throw null; }
-        public void FromNativeValue(byte* value) { }
+        public BStrStringMarshaller(string? str, System.Span<ushort> buffer) { }
+        public ushort* ToNativeValue() { throw null; }
+        public void FromNativeValue(ushort* value) { }
         public string? ToManaged() { throw null; }
         public void FreeNative() { }
     }

From e0ca27d900d80994cefa1ed0ba2b6e8eda9e643d Mon Sep 17 00:00:00 2001
From: Aaron Robinson <arobins@microsoft.com>
Date: Thu, 12 May 2022 09:51:57 -0700
Subject: [PATCH 09/11] Update
 src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs

Co-authored-by: Jan Kotas <jkotas@microsoft.com>
---
 .../Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs
index a62f7528473c15..786623eee3d0a1 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs
@@ -11,7 +11,7 @@ namespace System.Runtime.InteropServices.Marshalling
     /// Marshaller for BSTR strings
     /// </summary>
     [CLSCompliant(false)]
-    [CustomTypeMarshaller(typeof(string), BufferSize = 0x200,
+    [CustomTypeMarshaller(typeof(string), BufferSize = 0x100,
         Features = CustomTypeMarshallerFeatures.UnmanagedResources | CustomTypeMarshallerFeatures.TwoStageMarshalling | CustomTypeMarshallerFeatures.CallerAllocatedBuffer)]
     public unsafe ref struct BStrStringMarshaller
     {

From 57055aed2e60ea915c39595dfc25a2199864e09e Mon Sep 17 00:00:00 2001
From: Aaron Robinson <arobins@microsoft.com>
Date: Thu, 12 May 2022 12:18:13 -0700
Subject: [PATCH 10/11] Convert to use void* for BStr and Utf16 marshallers'
 native types.

---
 .../Marshalling/BStrStringMarshaller.cs        | 18 ++++++++++--------
 .../Marshalling/Utf16StringMarshaller.cs       | 13 +++++++------
 .../ref/System.Runtime.InteropServices.cs      | 10 +++++-----
 3 files changed, 22 insertions(+), 19 deletions(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs
index 786623eee3d0a1..b348ab27711a2f 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs
@@ -15,7 +15,7 @@ namespace System.Runtime.InteropServices.Marshalling
         Features = CustomTypeMarshallerFeatures.UnmanagedResources | CustomTypeMarshallerFeatures.TwoStageMarshalling | CustomTypeMarshallerFeatures.CallerAllocatedBuffer)]
     public unsafe ref struct BStrStringMarshaller
     {
-        private ushort* _ptrToFirstChar;
+        private void* _ptrToFirstChar;
         private bool _allocated;
 
         /// <summary>
@@ -46,6 +46,7 @@ public BStrStringMarshaller(string? str, Span<ushort> buffer)
                 return;
             }
 
+            ushort* ptrToFirstChar;
             int lengthInBytes = checked(sizeof(char) * str.Length);
 
             // A caller provided buffer must be at least (lengthInBytes + 6) bytes
@@ -54,7 +55,7 @@ public BStrStringMarshaller(string? str, Span<ushort> buffer)
             if (manualBstrNeeds > buffer.Length)
             {
                 // Use precise byte count when the provided stack-allocated buffer is not sufficient
-                _ptrToFirstChar = (ushort*)Marshal.AllocBSTRByteLen((uint)lengthInBytes);
+                ptrToFirstChar = (ushort*)Marshal.AllocBSTRByteLen((uint)lengthInBytes);
                 _allocated = true;
             }
             else
@@ -62,15 +63,16 @@ public BStrStringMarshaller(string? str, Span<ushort> buffer)
                 // Set length and update buffer target
                 byte* pBuffer = (byte*)Unsafe.AsPointer(ref MemoryMarshal.GetReference(buffer));
                 *((uint*)pBuffer) = (uint)lengthInBytes;
-                _ptrToFirstChar = (ushort*)(pBuffer + sizeof(uint));
+                ptrToFirstChar = (ushort*)(pBuffer + sizeof(uint));
             }
 
             // Confirm the size is properly set for the allocated BSTR.
-            Debug.Assert(lengthInBytes == Marshal.SysStringByteLen((IntPtr)_ptrToFirstChar));
+            Debug.Assert(lengthInBytes == Marshal.SysStringByteLen((IntPtr)ptrToFirstChar));
 
             // Copy characters from the managed string
-            str.CopyTo(new Span<char>(_ptrToFirstChar, str.Length));
-            _ptrToFirstChar[str.Length] = '\0'; // null-terminate
+            str.CopyTo(new Span<char>(ptrToFirstChar, str.Length));
+            ptrToFirstChar[str.Length] = '\0'; // null-terminate
+            _ptrToFirstChar = ptrToFirstChar;
         }
 
         /// <summary>
@@ -79,7 +81,7 @@ public BStrStringMarshaller(string? str, Span<ushort> buffer)
         /// <remarks>
         /// <seealso cref="CustomTypeMarshallerFeatures.TwoStageMarshalling"/>
         /// </remarks>
-        public ushort* ToNativeValue() => _ptrToFirstChar;
+        public void* ToNativeValue() => _ptrToFirstChar;
 
         /// <summary>
         /// Sets the native value representing the string.
@@ -88,7 +90,7 @@ public BStrStringMarshaller(string? str, Span<ushort> buffer)
         /// <remarks>
         /// <seealso cref="CustomTypeMarshallerFeatures.TwoStageMarshalling"/>
         /// </remarks>
-        public void FromNativeValue(ushort* value)
+        public void FromNativeValue(void* value)
         {
             _ptrToFirstChar = value;
             _allocated = true;
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/Utf16StringMarshaller.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/Utf16StringMarshaller.cs
index 7d77bedc19ff51..64fb70b3127025 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/Utf16StringMarshaller.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/Utf16StringMarshaller.cs
@@ -13,7 +13,7 @@ namespace System.Runtime.InteropServices.Marshalling
         Features = CustomTypeMarshallerFeatures.UnmanagedResources | CustomTypeMarshallerFeatures.TwoStageMarshalling)]
     public unsafe ref struct Utf16StringMarshaller
     {
-        private ushort* _nativeValue;
+        private void* _nativeValue;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Utf16StringMarshaller"/>.
@@ -32,10 +32,11 @@ public Utf16StringMarshaller(string? str)
             }
 
             // + 1 for null terminator
-            _nativeValue =  (ushort*)Marshal.AllocCoTaskMem((str.Length + 1) * sizeof(ushort));
+            ushort* nativeValue = (ushort*)Marshal.AllocCoTaskMem((str.Length + 1) * sizeof(char));
 
-            str.CopyTo(new Span<char>(_nativeValue, str.Length));
-            _nativeValue[str.Length] = '\0'; // null-terminate
+            str.CopyTo(new Span<char>(nativeValue, str.Length));
+            nativeValue[str.Length] = '\0'; // null-terminate
+            _nativeValue = nativeValue;
         }
 
         /// <summary>
@@ -44,7 +45,7 @@ public Utf16StringMarshaller(string? str)
         /// <remarks>
         /// <seealso cref="CustomTypeMarshallerFeatures.TwoStageMarshalling"/>
         /// </remarks>
-        public ushort* ToNativeValue() => _nativeValue;
+        public void* ToNativeValue() => _nativeValue;
 
         /// <summary>
         /// Sets the native value representing the string.
@@ -53,7 +54,7 @@ public Utf16StringMarshaller(string? str)
         /// <remarks>
         /// <seealso cref="CustomTypeMarshallerFeatures.TwoStageMarshalling"/>
         /// </remarks>
-        public void FromNativeValue(ushort* value) => _nativeValue = value;
+        public void FromNativeValue(void* value) => _nativeValue = value;
 
         /// <summary>
         /// Returns the managed string.
diff --git a/src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs b/src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs
index 8681fb03854048..263fc63b0a6b04 100644
--- a/src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs
+++ b/src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs
@@ -2079,7 +2079,7 @@ public void FromNativeValue(byte* value) { }
         public void FreeNative() { }
     }
     [System.CLSCompliant(false)]
-    [System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerAttribute(typeof(string), BufferSize = 0x200,
+    [System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerAttribute(typeof(string), BufferSize = 0x100,
         Features = System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerFeatures.UnmanagedResources
             | System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerFeatures.CallerAllocatedBuffer
             | System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerFeatures.TwoStageMarshalling )]
@@ -2087,8 +2087,8 @@ public unsafe ref struct BStrStringMarshaller
     {
         public BStrStringMarshaller(string? str) { }
         public BStrStringMarshaller(string? str, System.Span<ushort> buffer) { }
-        public ushort* ToNativeValue() { throw null; }
-        public void FromNativeValue(ushort* value) { }
+        public void* ToNativeValue() { throw null; }
+        public void FromNativeValue(void* value) { }
         public string? ToManaged() { throw null; }
         public void FreeNative() { }
     }
@@ -2207,8 +2207,8 @@ public void FreeNative() { }
     public unsafe ref struct Utf16StringMarshaller
     {
         public Utf16StringMarshaller(string? str) { }
-        public ushort* ToNativeValue() { throw null; }
-        public void FromNativeValue(ushort* value) { }
+        public void* ToNativeValue() { throw null; }
+        public void FromNativeValue(void* value) { }
         public string? ToManaged() { throw null; }
         public void FreeNative() { }
     }

From 2379671fd2748aa622f885c28ed35460a794cd69 Mon Sep 17 00:00:00 2001
From: Aaron R Robinson <arobins@microsoft.com>
Date: Thu, 19 May 2022 21:32:56 -0700
Subject: [PATCH 11/11] Review feedback

---
 .../Marshalling/BStrStringMarshaller.cs       |  1 +
 .../ref/System.Runtime.InteropServices.cs     | 28 +++++++++----------
 2 files changed, 15 insertions(+), 14 deletions(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs
index b348ab27711a2f..ce5a83a69e1abb 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshalling/BStrStringMarshaller.cs
@@ -106,6 +106,7 @@ public void FromNativeValue(void* value)
         {
             if (_ptrToFirstChar is null)
                 return null;
+
             return Marshal.PtrToStringBSTR((IntPtr)_ptrToFirstChar);
         }
 
diff --git a/src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs b/src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs
index 263fc63b0a6b04..6e39fb98a84d22 100644
--- a/src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs
+++ b/src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs
@@ -2078,20 +2078,6 @@ public void FromNativeValue(byte* value) { }
         public string? ToManaged() { throw null; }
         public void FreeNative() { }
     }
-    [System.CLSCompliant(false)]
-    [System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerAttribute(typeof(string), BufferSize = 0x100,
-        Features = System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerFeatures.UnmanagedResources
-            | System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerFeatures.CallerAllocatedBuffer
-            | System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerFeatures.TwoStageMarshalling )]
-    public unsafe ref struct BStrStringMarshaller
-    {
-        public BStrStringMarshaller(string? str) { }
-        public BStrStringMarshaller(string? str, System.Span<ushort> buffer) { }
-        public void* ToNativeValue() { throw null; }
-        public void FromNativeValue(void* value) { }
-        public string? ToManaged() { throw null; }
-        public void FreeNative() { }
-    }
     [System.CLSCompliantAttribute(false)]
     [System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerAttribute(typeof(System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerAttribute.GenericPlaceholder[]),
         System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerKind.LinearCollection, BufferSize = 0x200,
@@ -2113,6 +2099,20 @@ public void FromNativeValue(byte* value) { }
         public T[]? ToManaged() { throw null; }
         public void FreeNative() { }
     }
+    [System.CLSCompliant(false)]
+    [System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerAttribute(typeof(string), BufferSize = 0x100,
+        Features = System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerFeatures.UnmanagedResources
+            | System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerFeatures.CallerAllocatedBuffer
+            | System.Runtime.InteropServices.Marshalling.CustomTypeMarshallerFeatures.TwoStageMarshalling )]
+    public unsafe ref struct BStrStringMarshaller
+    {
+        public BStrStringMarshaller(string? str) { }
+        public BStrStringMarshaller(string? str, System.Span<ushort> buffer) { }
+        public void* ToNativeValue() { throw null; }
+        public void FromNativeValue(void* value) { }
+        public string? ToManaged() { throw null; }
+        public void FreeNative() { }
+    }
     [System.AttributeUsageAttribute(System.AttributeTargets.Struct)]
     public sealed partial class CustomTypeMarshallerAttribute : System.Attribute
     {